Vehicle radar sensing system with enhanced angle resolution using synthesized aperture

ABSTRACT

A sensing system for a vehicle includes at least one radar sensor disposed at the vehicle and having a field of sensing exterior of the vehicle. The radar sensor includes multiple transmitting antennas and multiple receiving antennas. The transmitting antennas transmit signals and the receiving antennas receive the signals reflected off objects. Multiple scans of radar data sensed by the radar sensor are received at a control, and a vehicle motion estimation is received at the control. The control, responsive to received scans of sensed radar data, detects the presence of objects within the field of sensing of the radar sensor. The control, responsive to the received scans of sensed radar data and the received vehicle motion estimation, synthesizes a virtual aperture and matches objects detected in the scans and determines a separation between detected objects by tracking the detected objects over two or more scans.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims the filing benefits of U.S. provisional application Ser. No. 62/555,222, filed Sep. 7, 2017, which is hereby incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to a vehicle sensing system for a vehicle and, more particularly, to a vehicle sensing system that utilizes one or more sensors at a vehicle to provide a field of sensing at or around the vehicle.

BACKGROUND OF THE INVENTION

Use of imaging sensors or ultrasonic sensors or radar sensors in vehicle sensing systems is common and known. Examples of such known systems are described in U.S. Pat. Nos. 8,013,780 and 5,949,331 and/or U.S. publication No. US-2010-0245066 and/or International Publication No. WO 2011/090484, which are hereby incorporated herein by reference in their entireties.

SUMMARY OF THE INVENTION

The present invention provides a driver assistance system or sensing system for a vehicle that utilizes a sensor module or system disposed at the vehicle and comprising at least one radar sensor disposed at the vehicle and having a field of sensing exterior of the vehicle. The at least one radar sensor comprises multiple Tx (transmitters) and Rx (receivers) to provide high definition, fine resolution in azimuth and/or elevation to determine high definition radar reflection responses for objects and surfaces detected by the system. The system includes a control, where outputs (such as radar data acquisitions of multiple scans) of the at least one radar sensor are communicated to the control, and where the control, responsive to the outputs of the at least one radar sensor, detects the presence of objects in the field of sensing of the radar sensor or sensors. The system uses multiple scans to synthesize a virtual aperture using the vehicle position change between the scans. The system provides enhanced accuracy in determining the location of a detected object relative to the vehicle and sensor(s).

The present invention provides a means to substantially or drastically improve the ability of an automotive radar system to distinguish different targets in the angle dimension. The system synthesizes a virtual aperture using the vehicle movement between scans. This Synthetic Aperture (SA) or synthesized aperture can be quite long depending on the number of integrated scans, vehicle velocity and scan dwell time. In order to be able to separate at least two targets within a nominal angle resolution, the minimum number of scans to be integrated is three.

These and other objects, advantages, purposes and features of the present invention will become apparent upon review of the following specification in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a vehicle with a sensing system that incorporates a radar sensor in accordance with the present invention;

FIG. 2 is a graph showing azimuth angle resolution comparison between the present invention and a single scan estimation for a target with a SNR of 20 dBs; and

FIG. 3 is a graph showing azimuth angle resolution comparison between the present invention and a single scan estimation for a target with a SNR of 10 dBs.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A vehicle sensing system, such as a driver assist system, object detection system, parking assist system and/or alert system, operates to capture sensing data exterior of the vehicle and may process the captured data to detect objects or other vehicles at or near the equipped vehicle and in the predicted path of the equipped vehicle, such as to assist a driver of the equipped vehicle in maneuvering the vehicle in a forward or rearward direction or to assist the driver in parking the vehicle in a parking space. The system includes a processor that is operable to receive sensing data from one or more sensors and to provide an output to a control that, responsive to the output, generates an alert or controls an accessory or system of the vehicle, or highlights or overlays an alert on a display screen (that may be displaying video images captured by a single rearward viewing camera or multiple cameras providing forward, side or 360 degree surround views of the area surrounding the vehicle during a reversing or low speed maneuver of the vehicle).

Referring now to the drawings and the illustrative embodiments depicted therein, a vehicle 10 includes an driver assistance system or sensing system 12 that includes at least one radar sensor unit, such as a forward facing radar sensor unit 14 (and the system may optionally include multiple exterior facing sensors, such as multiple exterior facing radar sensors or cameras or other sensors, such as a rearward facing sensor at the rear of the vehicle, and a sideward/rearward facing sensor at respective sides of the vehicle), which sense regions exterior of the vehicle. The sensing system 12 includes a control or electronic control unit (ECU) or processor that is operable to process data captured by the sensor or sensors and may detect objects or the like. The data transfer or signal communication from the sensor to the ECU may comprise any suitable data or communication link, such as a vehicle network bus or the like of the equipped vehicle.

Some automotive radars use MIMO (Multiple Input Multiple Output) techniques to create an effective virtual antenna aperture, which is significantly larger than the real antenna aperture, and delivers much better angular resolution than conventional radars, such as, for example, conventional scanning radars.

Algorithms to estimate target positioning on automotive radar typically either use a coherent single scan or an incoherent set of scans. When using a single scan coherently, the algorithm uses the complex value of the different antenna phase centers for a certain range and carry out a beamforming (BF) in order to obtain the angular position of the target. In this case, the ability to separate two targets separated by a narrow angle is driven by the physical antenna array size. The second type of target positioning utilizes a set of scans incoherently, and receives as inputs a set of target list outputs from different scans (similar to the first example). In this case, the resolution is not improved per se. Two targets close by in angle will be reported as two separate targets only when they present sufficient difference in angle. For example, two vehicles far away that are in adjacent lanes may be seen as a single vehicle. However, as they get closer to the subject vehicle, they may eventually present enough angle difference to be seen or sensed as two separate targets. Thus, at that moment, the system identifies as two targets what it was earlier or previously sensing as just one target.

The system of the present invention substantially improves the ability of an automotive radar to distinguish different targets in the angle dimension by synthesizing a virtual aperture using the car movement between scans. This allows the system to use coherent integration through a different set of scans in order to distinguish targets close by in angle in just a few scans. To this end, the system of the present invention generates a virtual array by the vehicle position change between scans. For example, a vehicle moving at 80 km/h with a radar scan time of 30 ms yields in a virtual array size of 0.67 meters with two scans (that is, the vehicle will travel 0.67 meters between scans), 1.33 m using 3 scans and 6 m using 10 scans. Thus, the formed virtual array with several phase centers is significantly larger with respect to the physical antenna array size.

The separation between contiguous phase centers is related to distance travelled by the vehicle between scans. That distance is most likely large enough to get grating lobes within a few degrees. Thus, the use of this technique requires knowledge in advance in order to avoid confusing main lobes with grating lobes. This advanced knowledge may be provided by a single scan Angle of Arrival (AoA) estimation. This implies that the maximum AoA estimation error is lower than the separation between the main lobe and the grating lobe.

The system of the present invention receives as input an ego motion estimation (an estimation of the motion of the measuring sensor disposed at the equipped or subject vehicle), a time stamp of each data acquisition or scan, a detection list for each scan with detected targets position, Doppler velocity and complex value after beamforming, and a sensor position of the measuring sensor with respect to the vehicle.

The dataflow includes matching the targets between scans. For every target, there is a series of complex values which come from the detection list of every scan. For every target and scan, this value is obtained after beamforming.

The next step is to “flatten” the phases by taking into account the vehicle movement and the estimated target positioning by the scans. This “phase flattening” can be done as a geometric approach by taking into account the different positions of the radar sensor and targets. The remaining phases are relative to the first position which will be 0 degrees.

Then, the system performs an assessment to check if it is possible to estimate the AoA without ambiguity. In essence, this tests if the scans maximum AoA error is within grating lobes. Targets with high SNR are more likely to be solved unambiguously. An AoA estimation is applied over the complex series within the angle dynamic range between grating lobes. Finally, the system reports the found targets using the long synthetic aperture (SA). This SA may be quite long depending on the number of integrated scans, vehicle velocity and scan dwell time. In order to be able to separate at least two targets within the nominal angle resolution, ideally the number of scans integrated is at least three.

For example, for an Azimuth dimension, the following parameters may be taken into account: vehicle velocity of 80 km/h, scan time of 30 ms, sensor frequency of 79 GHz (wavelength of 3.8 mm), 7 physical phase centers, and a 2 wavelength separation between physical phase centers. FIGS. 2 and 3 show the resolution improvement vs nominal Azimuth Angle Resolution assuming 20 dBs SNR (FIG. 2) and 10 dBs SNR (FIG. 3).

The curve A is the nominal resolution for different AoA and taking into account the single scan physical aperture. The accuracy is plotted as a solid line B and a dashed line C for one sigma and three sigmas, respectively. The line D represents the separation between grating lobes versus AoA. Thus, the SA Phase Unambiguous Region is defined as the region where three times sigma is below the grating lobe separation curve D. Finally, an example resolution is given by standard beamforming with a SA using three scans (see solid line E) and ten scans (see dashed line F).

As can be seen with reference to FIGS. 2 and 3, targets with a higher SNR show a wider angle Unambiguous Region (the region to the left of the vertical line in FIGS. 2 and 3) than weak targets or targets with a lower SNR. The resolution power quickly falls below 1 degree without using any super-resolution estimation method. As an example, an SA with 10 scans may separate targets around approximately 5 degrees of AoA with 0.18 degree resolution employing a simple beamforming.

The system of the present invention thus substantially improves the ability of an automotive radar to distinguish different targets in the angle dimension. The system synthesizes a virtual aperture using the vehicle movement between scans. The Synthetic Aperture (SA) can be quite long depending on the number of integrated scans, vehicle velocity and scan dwell time. In order to be able to separate at least two targets within the nominal angle resolution, the minimum number of scans to be integrated is preferably three.

The system may provide an output for a driving assist system of the vehicle, such as one or more of (i) automated parking, (ii) blind spot detection, (iii) cross traffic alert, (iv) lane change assist, (v) lane merge assist, (vi) automatic emergency braking, (vii) pedestrian detection, (viii) turn assist, (ix) terrain management, (x) collision mitigation and (xi) intersection collision mitigation. Optionally, the output may be provided to an autonomous vehicle control system.

For autonomous vehicles suitable for deployment with the system of the present invention, an occupant of the vehicle may, under particular circumstances, be desired or required to take over operation/control of the vehicle and drive the vehicle so as to avoid potential hazard for as long as the autonomous system relinquishes such control or driving. Such occupant of the vehicle thus becomes the driver of the autonomous vehicle. As used herein, the term “driver” refers to such an occupant, even when that occupant is not actually driving the vehicle, but is situated in the vehicle so as to be able to take over control and function as the driver of the vehicle when the vehicle control system hands over control to the occupant or driver or when the vehicle control system is not operating in an autonomous or semi-autonomous mode.

Typically an autonomous vehicle would be equipped with a suite of sensors, including multiple machine vision cameras deployed at the front, sides and rear of the vehicle, multiple radar sensors deployed at the front, sides and rear of the vehicle, and/or multiple lidar sensors deployed at the front, sides and rear of the vehicle. Typically, such an autonomous vehicle will also have wireless two way communication with other vehicles or infrastructure, such as via a car2car (V2V) or car2x communication system. The forward viewing camera and/or the sensor of the lane determining system may comprise one of the cameras and/or one of the sensors of the autonomous vehicle control system.

The sensing system may include a machine vision system (comprising at least one exterior viewing camera disposed at the vehicle and an image processor for processing image data captured by the at least one camera), where information is shared between the stereo radar and the machine vision system.

The system may include two or more individual radars, having individual or multiple Tx (transmitters) and Rx (receivers) on an antenna array, and may utilize aspects of the systems described in U.S. Pat. Nos. 9,753,121; 9,689,967; 9,599,702; 9,575,160; 9,146,898; 9,036,026; 8,027,029; 8,013,780; 6,825,455; 7,053,357; 7,408,627; 7,405,812; 7,379,163; 7,379,100; 7,375,803; 7,352,454; 7,340,077; 7,321,111; 7,310,431; 7,283,213; 7,212,663; 7,203,356; 7,176,438; 7,157,685; 6,919,549; 6,906,793; 6,876,775; 6,710,770; 6,690,354; 6,678,039; 6,674,895 and/or 6,587,186, and/or International Publication Nos. WO 2018/007995 and/or WO 2011/090484, and/or U.S. Publication Nos. US-2018-0231635; US-2018-0045812; US-2018-0015875; US-2017-0356994; US-2017-0315231; US-2017-0276788; US-2017-0254873; US-2017-0222311, which are hereby incorporated herein by reference in their entireties.

Changes and modifications in the specifically described embodiments can be carried out without departing from the principles of the invention, which is intended to be limited only by the scope of the appended claims, as interpreted according to the principles of patent law including the doctrine of equivalents. 

The invention claimed is:
 1. A sensing system for a vehicle, said sensing system comprising: at least one radar sensor disposed at a vehicle equipped with said sensing system and having a field of sensing exterior of the equipped vehicle; wherein said at least one radar sensor comprises multiple transmitting antennas and multiple receiving antennas, and wherein said transmitting antennas transmit signals and said receiving antennas receive the signals reflected off objects; a control comprising a processor, wherein multiple scans of radar data sensed by said at least one radar sensor are received at said control and processed at said processor; wherein a vehicle motion estimation is received at said control; wherein said control, responsive to processing at the processor of the received multiple scans of sensed radar data, detects a presence of two or more objects exterior the equipped vehicle and within the field of sensing of said at least one radar sensor; and wherein said control, responsive at least in part to processing at the processor of the received multiple scans of sensed radar data and the received vehicle motion estimation, synthesizes a virtual aperture and matches objects detected in the multiple scans and determines a separation between two detected objects by tracking the detected objects over two or more scans.
 2. The sensing system of claim 1, wherein the received multiple scans of sensed radar data comprises radar data acquisitions for at least three consecutive scans by said at least one radar sensor.
 3. The sensing system of claim 2, wherein each radar data acquisition is time stamped.
 4. The sensing system of claim 3, wherein said control receives a detection list for each scan with detected objects' positions, Doppler velocities and complex values.
 5. The sensing system of claim 4, wherein said control determines angles toward detected objects responsive to a sensor position of said at least one radar sensor at the equipped vehicle.
 6. The sensing system of claim 2, wherein said control flattens phases by taking into account the vehicle motion and estimated object positioning by the scans.
 7. The sensing system of claim 6, wherein said control determines if a maximum angle of arrival error of the scans is within grating lobes emitted by the transmitting antennas.
 8. The sensing system of claim 7, wherein said control applies an angle of arrival estimation over a complex series within an angle dynamic range between the grating lobes.
 9. The sensing system of claim 1, wherein a vision system of the equipped vehicle comprises at least one exterior viewing camera disposed at the equipped vehicle and an image processor for processing image data captured by the at least one exterior viewing camera, and wherein information is shared between said sensing system and the vision system of the equipped vehicle.
 10. The sensing system of claim 1, wherein said sensing system comprises two or more individual radar sensors, each having multiple transmitting antennas and receiving antennas on an antenna array, and wherein information is shared between the individual radar sensors operating in stereo to determine high definition radar reflection responses for objects detected by said sensing system.
 11. The sensing system of claim 1, wherein said at least one radar sensor is disposed at a front portion of the equipped vehicle and senses forward of the equipped vehicle.
 12. The sensing system of claim 1, wherein said sensing system provides an output for at least one driving assist system function selected from the group consisting of (i) automated parking, (ii) blind spot detection, (iii) cross traffic alert, (iv) lane change assist, (v) lane merge assist, (vi) automatic emergency braking, (vii) pedestrian detection, (viii) turn assist, (ix) terrain management, (x) collision mitigation and (xi) intersection collision mitigation.
 13. A sensing system for a vehicle, said sensing system comprising: at least one radar sensor disposed at a vehicle equipped with said sensing system and having a field of sensing exterior of the equipped vehicle; wherein said at least one radar sensor comprises multiple transmitting antennas and multiple receiving antennas, and wherein said transmitting antennas transmit signals and said receiving antennas receive the signals reflected off objects; a control comprising a processor, wherein multiple scans of radar data sensed by said at least one radar sensor are received at said control and processed at said processor; wherein the received multiple scans of sensed radar data comprises radar data acquisitions for at least three consecutive scans by said at least one radar sensor; wherein a vehicle motion estimation is received at said control; wherein said control, responsive to processing at the processor of the received multiple scans of sensed radar data, detects a presence of two or more objects exterior the equipped vehicle and within the field of sensing of said at least one radar sensor; wherein said control, responsive at least in part to processing at the processor of the received multiple scans of sensed radar data and the received vehicle motion estimation, synthesizes a virtual aperture and matches objects detected in the multiple scans and determines a separation between two detected objects by tracking the detected objects over two or more scans; and wherein said sensing system provides an output for at least one driving assist system function selected from the group consisting of (i) automated parking, (ii) blind spot detection, (iii) cross traffic alert, (iv) lane change assist, (v) lane merge assist, (vi) automatic emergency braking, (vii) pedestrian detection, (viii) turn assist, (ix) terrain management, (x) collision mitigation and (xi) intersection collision mitigation.
 14. The sensing system of claim 13, wherein said control receives a detection list for each scan with detected objects' positions, Doppler velocities and complex values.
 15. The sensing system of claim 13, wherein said at least one radar sensor is disposed at a front portion of the equipped vehicle and senses forward of the equipped vehicle.
 16. The sensing system of claim 13, wherein said sensing system comprises two or more individual radar sensors, each having multiple transmitting antennas and receiving antennas on an antenna array, and wherein information is shared between the individual radar sensors operating in stereo to determine high definition radar reflection responses for objects detected by said sensing system.
 17. A sensing system for a vehicle, said sensing system comprising: at least one radar sensor disposed at a vehicle equipped with said sensing system and having a field of sensing exterior of the equipped vehicle; wherein said at least one radar sensor comprises multiple transmitting antennas and multiple receiving antennas, and wherein said transmitting antennas transmit signals and said receiving antennas receive the signals reflected off objects; a control comprising a processor, wherein multiple scans of radar data sensed by said at least one radar sensor are received at said control and processed at said processor; wherein a vehicle motion estimation is received at said control; wherein said control, responsive to processing at the processor of the received multiple scans of sensed radar data, detects a presence of two or more objects exterior the equipped vehicle and within the field of sensing of said at least one radar sensor; wherein said control, responsive at least in part to processing at the processor of the received multiple scans of sensed radar data and the received vehicle motion estimation, synthesizes a virtual aperture and matches objects detected in the multiple scans and determines a separation between two detected objects by tracking the detected objects over two or more scans; wherein said control flattens phases by taking into account the vehicle motion and estimated object positioning by the scans, and wherein said control determines if a maximum angle of arrival error of the scans is within grating lobes emitted by the transmitting antennas, and wherein said control applies an angle of arrival estimation over a complex series within an angle dynamic range between the grating lobes; and wherein said sensing system provides an output for at least one driving assist system function selected from the group consisting of (i) automated parking, (ii) blind spot detection, (iii) cross traffic alert, (iv) lane change assist, (v) lane merge assist, (vi) automatic emergency braking, (vii) pedestrian detection, (viii) turn assist, (ix) terrain management, (x) collision mitigation and (xi) intersection collision mitigation.
 18. The sensing system of claim 17, wherein each radar data acquisition is time stamped.
 19. The sensing system of claim 17, wherein said control receives a detection list for each scan with detected objects' positions, Doppler velocities and complex values.
 20. The sensing system of claim 17, wherein said at least one radar sensor is disposed at a front portion of the equipped vehicle and senses forward of the equipped vehicle. 